In general, dialysis treatment is performed by using a dialysis treatment apparatus including a blood circuit for extracorporeally circulating the blood of a patient, a dialyzer connected to a halfway point of the blood circuit, a peristaltic blood pump, and a dialysis-apparatus body capable of performing ultrafiltration while performing hemodialysis treatment in which dialysate is introduced into or delivered from the dialyzer. Typically, dialysis treatment performed with such a dialysis treatment apparatus continues for about four hours and is given every other day. Accordingly, impurities accumulated in two days need to be removed in about four hours. Therefore, the hemodynamics of the patient during the treatment changes significantly. Particularly, it is important to efficiently and assuredly prevent the decrease in blood pressure caused by the removal of excessive water (ultrafiltration).
To solve the above problem, some apparatuses have hitherto been proposed in which the hematocrit value (the volume fraction of blood-cell components in the blood) of the blood of the patient during dialysis treatment is detected, and the rate of change in the circulating blood volume (ΔBV) of the patient is calculated from the detected hematocrit value and is monitored. According to another proposal (see PTL 1, for example), not only information, such as the rate of change in the circulating blood volume (ΔBV), obtained from the blood that is under extracorporeal circulation but also noninvasive vital signs of the patient observed during the blood purification treatment are detected successively, and the detected vital signs are displayed, whereby any changes in the condition of the patient (particularly, a decrease in blood pressure) can be notified efficiently and assuredly.